This invention has for its object a method for inspecting the integrity of the filter tip cigarette wrapper, that is for detecting and indicating, cigarette by cigarette, the defects of the wrapper. These defects comprise substantially leaks, breaks and paper wrapper sealing discontinuities, or apertues, breaks in the tipping band which attaches the filter plug to the cigarette, as well as wrapping and sealing defects of the said tipping band.
In known electropneumatic cigarette inspection devices, all the defects resulting from leaks in the cigarette wrapper are totally detected, with a single test consisting in applying a calibrated pressure or vacuum at one end of the cigarette while the other end is kept closed by a rubber pad, and in detecting, after a reasonable interval of time, the pressure drop which reveals undue air losses through the wrapper.
This drop, which is applied to known electropneumatic transducers, generates correlative inspection signals which, read with a time scanning procedure and opportunely stored, will be subsequently used to control a device which rejects the defective cigarettes.
This electropneumatic inspection constitutes, however, a principle of selection which has only a first approximation validity. In fact, it cannot take into account the permeability proper of the type of filter and of the cut tobacco, the degree of condensation of which in the rod varies generally within large limits in a random manner; neither can it take into account the fact that the wrapper and the filter tipping material, even if integral, presents already a natural permeability to the air, which generally varies from one cigarette to another, and this variability masks the presence of air loss defects which it would be desired to detect, because it is summed up with them during the test.